<!DOCTYPE html>
<!-- This is an expanded version of external/wpt/css/cssom-view/background-change-during-smooth-scroll.html,
     to ensure the test actually exercises the code path to be covered. -->
<style>
#container {
  width: 200px;
  height: 200px;
  overflow: scroll;
  background: white;
}

#content {
  width: 7500px;
  height: 7500px;
}
</style>
<script src="../../resources/testharness.js"></script>
<script src="../../resources/testharnessreport.js"></script>
<script>
// Disable PreferCompositingToLCDText so that changing background opaqueness
// can change composited scrolling status.
if (window.internals)
  internals.settings.setPreferCompositingToLCDTextEnabled(false);

var t = async_test('overflow-scroll-loses-composited-scrolling');

function startSmoothScroll() {
  t.step(() => {
    if (window.internals) {
      assert_true(internals.layerTreeAsText(document).includes('container'),
                  'container should be composited');
    }
  });
  var scrollToOptions = {behavior: "smooth", top: 6000};
  container.scrollTo(scrollToOptions);
  requestAnimationFrame(preventCompositedScrolling);
}

function preventCompositedScrolling() {
  container.style.background = "transparent";
  requestAnimationFrame(() => {
    t.step(() => {
      if (window.internals) {
        assert_false(internals.layerTreeAsText(document).includes('container'),
                     'container should not be composited');
      }
    });
    waitForSmoothScrollEnd();
  });
}

function waitForSmoothScrollEnd() {
  if (container.scrollTop == 6000) {
    t.done();
  } else {
    window.requestAnimationFrame(waitForSmoothScrollEnd);
  }
}

onload = () => {
  requestAnimationFrame(startSmoothScroll);
}
</script>
<div id="container">
  <div id="content">Content</div>
</div>
